In a portable telephone, generally, a housing accommodates a receiving speaker, and a through hole is formed to extend from the receiving speaker accommodating portion to the outside. When speaking over the telephone, the user applies his ear over the through hole, and speaks while listening to the output sound produced by the receiving speaker through the through hole. As the structure of the through hole, the following ones have been proposed.
As the first prior art, reference 1 (Japanese Patent Laid-Open No. 10-304036) discloses a technique which forms an earpiece portion to have a projecting structure that projects from a housing, and provides the first through hole, which is directed to the ear hole, and the second through (pre-leak portion), which is open to the outer space that does not correspond to the ear hole, when the user's ear pinna opposes the first through hole. According to this technique, as the earpiece portion is provided with the pre-leak portion through which the sound leaks appropriately, even if the gap between the earpiece portion and the ear changes, the influence of the change can be moderated.
As the second prior art, reference 2 (Japanese Patent Laid-Open No. 2000-244618) discloses a technique of a folding portable telephone which includes a through hole extending from a receiving speaker to an earpiece portion, and in which a groove is formed to extend from the opening of the through hole to the end of a housing. According to this technique, the receiving speaker can also serve as a ringer. By forming the groove to extend from the opening of the through hole to the end of the housing, the sound leaks appropriately, stabilizing the sound quality.
As the third prior art, reference 3 (Japanese Patent Laid-Open No. 2001-230841) discloses a technique which provides the first through hole formed in a housing in front of a receiving speaker (sound source), a voice guide structure which guides the voice from a surface other than the front direction of the receiving speaker to the outside, and the second through hole formed to emit the sound to the outside of the housing, so that the generated voice is emitted to the outside from surfaces in two directions. According to this technique, the voice from the receiving speaker can be emitted to the outside of the housing efficiently without increasing the power of the receiving speaker or increasing the voltage applied to the receiving speaker, thus increasing the sound pressure of the voice.